An electrocardiogram (ECG or, sometimes, EKG) signal is an electrical signal indicative of changes in electrical potential during a heartbeat, or contraction of the heart. ECG signals include features corresponding to certain aspects of each heartbeat and are used to diagnose cardiac activity abnormalities. One such feature is the R-wave which is manifested as a positive voltage spike in the ECG signal coincident with a ventricular contraction.
Various medical diagnostic and treatment apparatus require detection of the time of occurrence of the R-waves of a patient's ECG signal, including heart rate monitors and heart rate variability monitors. Heart rate variability monitors refer to a class of instruments with which changes in heartbeat rate are measured.
Conventional R-wave detection is typically achieved with a threshold detection scheme by which the ECG signal is compared to a threshold value, with the occurrence of the ECG signal exceeding the threshold indicating the occurrence of an R-wave. R-wave detection is complicated by the inherent noise and other artifacts typically associated with an ECG signal. For this reason, the ECG signal is typically filtered prior to comparison with the threshold value.
The threshold detection method of detecting R-waves is often suitable for use in heart rate monitors, since such monitors generally provide a gross measure of heart rate which is subject to drift. However, threshold detection for detecting R-waves is less satisfactory for use in heart rate variability monitors, since detection of precise R-wave times is critical to providing an accurate heart rate variability indication.
In one conventional heart rate variability monitor, sold by Boston Medical Technologies under the product name HRView.TM. versions I and II, R-wave detection is achieved with a combination of filtering, threshold detection and operator interaction. Once "approximate" R-wave locations are detected by threshold detection, the operator views the ECG signal and approximate R-wave locations on a display and is able to remove R-wave detections which are likely to be false based on some criteria, such as the detections being too close in time to other detections. The user is also able to view a heart rate variability signal (i.e., heart rate versus time) generated in response to the detected R-waves and remove any heart rate variations which are likely to be false based on some criteria, such as the magnitude of the variation. This technique is referred to as "splining" since, in response to a user's indication that a particular heart rate variation exceeds some criteria, the heart rate variability signal is "splined," so as to bridge the signal across the particular heart rate variation.
It would be desirable to provide apparatus and techniques for detecting R-wave events with improved accuracy, particularly for use in heart rate variability monitors which rely heavily on precise R-wave detection.